1. Field of Invention
The present disclosure relates generally to a method of affixing together an aircraft skin and frame. More specifically, the present disclosure concerns coupling an aircraft skin and frame with a temporary fastener dining a step of assembly and removing the fastener
2. Description of Prior Art
Much of the external surface of an aircraft is formed by applying a skin and anchoring it over an underlying substrate, such as a structure. When using mechanical fasteners to attach an outer skin to a rib or other structure, a liquid shim is typically applied between the structure and skin to eliminate gaps or other differences between the two parts. Multiple fasteners are also typically inserted through the skin and underlying structure to further eliminate any gaps between the skin and the structure. FIG. 1 schematically represents in a partial side sectional view a series of steps that may be used when applying an aircraft skin to a structure. Sequential steps are represented adjacent one another and identified with one of identifier letters A-F and a respective curved bracket. Step A depicts the skin 11 positioned over the structure 13 and aligned with preset index pins (not shown). A drill 16 is inserted through the skin 11 via a pilot hole 15 for forming a transfer hole 17 into the underlying structure 13. A section of skin 11 and corresponding structure 13 may include multiple pilot and transfer holes 15, 17.
After the transfer holes 17 are formed within the structure 13 the skin 11 may be lifted from the structure 13 and then a mask 21 applied to the skin and a shim material 19 applied onto the structure 13 on its surface on which the skin 11 is attached. The mask 21 can be used for preventing the shim material from attaching to the skin 11 and pre-securing it to the structure 13. The skin 11 with a film mask 21 and structure 13 with an applied shim 19 is represented in step B. In step C, a clamp 23 is shown inserted into the corresponding pilot and transfer holes 15, 17. As shown, the clamp 23 includes a shaft with a tip at one end having a width greater than the hole 15, 17 diameter, thus preventing the shaft from moving further upward. The clamp 23 also includes a mandrel shown secured around the shaft for compressing together the skin 11 and structure 13. Depending on the number of pilot and transfer holes 15, 17; a clamp 23 may be provided in every fourth or fifth hole. The compressive force squeezes out and extrudes excess shim 19 material that may have been present on the structure 13. Depending on the shim 19 material, a period of time is required for it to cure before the clamp 23 can be removed. After removing the clamp 23, a full-size drill (not shown) is used to bore out the transfer and pilot holes 15, 17 to create a full-sized bore 18 extending through the skin 11 and structure 13.
In step D, a full-sized clamp 25 is inserted within the full-sized bore 18 and compressive pressure again applied to the skin 11 and structure 13 to remove yet more shim 19 material. The full-sized clamp 25 can be removed after further curing of the shim 19 material. The skin 11 is taken away from the structure 13 and the mask 21 removed from the skin 11. In step E, a nut 27 is attached on the undersurface of the structure 13 and a setup bolt 29 is inserted within the bore 18 threadingly fastened to the nut 27. This provides an attachment force between the skin 11 and structure 13 so that an automatic drill 31 with associated drill bit 33 can automatically bore additional holes 35 through the skin 11 and structure 13. Clamps 25 are replaced with the setup bolts 29 prior to auto-drill because their size interferes with the drilling process.
In step F, additional nuts 27 are secured to the structure 13 bottom side. The skin 11 and structure 13 can be permanently attached by inserting permanent bolts 37 through the additional holes 35 and mating with the bolts 37. It should be pointed out that the clamp 25 is removed and replaced with the temporary setup bolt 29 to allow the automatic drill assembly to move unobstructed on the skin 11 surface.
The liquid shim 19 is allowed to harden before drilling full-size holes for setup bolts 29, which usually takes six to eight hours but requires the skin 11 to be removed to install setup bolts 29. Although drilling operations can begin after the six- to eight-hour cure, the risk associated with removing the skin 11 before the shim 19 has cured for twenty-four hours is too great. Therefore, practice typically requires that a full twenty-four hours of curing take place before the skin 11 can be removed to allow setup bolt 29 installation.